Effect of Hydrogen on Silicon Nitrides Formation by Microwave Excited Plasma Enhanced Chemical Vapor Deposition

1. Introduction

 High quality silicon nitride films (SiNx) formed at low temperature is strongly required because new materials such as Ge, high-k gate dielectrics, gate electrodes metals, etc. are introduced in advanced integrated circuit[1, 2].

The gas composition is very important for reducing process temperature of PECVD. We have reported the SiH₄ flow rate is most important parameter for controlling the deposition rate and the film quality in the PECVD using N₂, H₂, SiH₄ gasses. The deposition rate strongly depends on the SiH₄ flow rate; however the film quality was degraded with the increase of the flow rate [3]. The other parameters are considered to be also important in the PECVD. In this presentation, we describe effect of hydrogen on SiNx formation by the PECVD.

 2. Experimental

After native oxide was removed of silicon surface by HF solution, silicon nitride was deposited. The temperature set at 400 ̊C. Ar gas was used as the plasma excitation, and SiH₄/N₂/H₂ mixture gases were used for the source gases. The microwave power, the deposition pressure were 2000 W and 1.7 Pa, respectively. The flow rates of SiH₄, N₂, and Ar were 0.5, 75, and 20 sccm, respectively. The gas flow rate of H₂was varied from 0 to 45 sccm. The film density were measured by the X-ray reflectometry (XRR), and the N-H bonds in SiNx films were measured by Fourier transform infrared spectroscopy (FTIR), respectively.

 3. Results and discussions

Fig. 1 shows the deposition rate and refractive index of SiNx films as a function of H₂ flow rate. The deposition rates for all H₂ flow rates are almost the same and the refractive index increases with H₂ flow rate in H₂ flow rate less than 15 sccm, and the index decreases with H₂ flow rate in the flow rate larger than 15 sccm. We have reported that the deposition rate strongly depends on the SiH₄ flow rate and the deposition rate is proportional to the SiH₄ flow rate and the film quality degrades as the increase of SiH₄ flow rate in this PECVD [3]. This suggests that the film quality are controlled by the H₂flow rate without the deposition rate.

Fig. 2 shows the film density of SiNx films measured by XRR for various H₂ flow rates. The density is independent of the H₂ flow rates. Fig. 3 shows the N-H bond concentration measured by FTIR for various H₂ flow rates. The N-H bond concentration of 0 sccm case is much less than the others, and the concentration of other cases are almost the same. The Si/N ratio of SiNx measured by XPS of 0sccm case is 1-2 % less than the others. It is considered that the hydrogen effectively dissociate the SiH₄ gas and makes the nitridation species (NHx), as the result, the hydrogen improves the reaction efficiency of SiH₄and NHx.

 4. Acknowledgement

This work was partially supported by JSPS KAKENHI Grant Number 22000010 and the synchrotron radiation experiments were performed at the BL46XU of SPring-8 with the approval of JASRI (Proposal No. 2012B1725).

 5. References

[1] E. Sleeckx, et al, Microelectronics Reliability 45, p. 865, 2005.

[2] Y. Jong-Ho et al.,  VLSI Tech. 2003, p. 55.

[3] Y. Nakao, et al., SSDM 2011, p. 905.